Apparatus and method for reducing test resources in testing DRAMS

ABSTRACT

An apparatus and a method are disclosed for reducing the pin driver count required for testing computer memory devices, specifically Rambus DRAM, while a die is on a semiconductor wafer. By reducing the pin count, more DRAMs can be tested at the same time, thereby reducing test cost and time. One preferred embodiment utilizes a trailing edge of a precharge clock to select a new active bank address, so that the address line required to select a new active address does not have to be accessed at the same time as the row lines.

RELATED APPLICATIONS

This present application is a continuation of U.S. Patent ApplicationSer. No. 09/653,112, filed on Aug. 31, 2000, now U.S. Pat. No.6,854,079, issued Feb. 8, 2005, which is a continuation-in-partapplication of U.S. Pat. Application Ser. No. 09/454,808, filed on Dec.3, 1999, now U.S. Pat. No. 6,530,045, issued on Mar. 4, 2003, theentireties of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to semiconductor wafer testing and moreparticularly to an apparatus and method for reducing the pin countnecessary to test Rambus dynamic random access memory (RDRAM).

2. Description of the Related Art

Rambus DRAM (RDRAM) is a general-purpose, high-performance,packet-oriented dynamic random-access memory (DRAM) device suitable foruse in a broad range of applications, including computer memory,graphics, video, and other applications. FIG. 1 schematicallyillustrates an RDRAM device 10 interconnected with a central processingunit (CPU) 11 as part of a typical computer system. The RDRAM device 10receives clock signals 12, control logic signal 14 and addressinformation 16 from the CPU 11 via a controller 20. Data 17 is writtento and read from the RDRAM 10.

FIG. 2 is a block diagram illustrating one 144 Mbit RDRAM configurationin the normal mode. The RDRAM comprises two major blocks: a “core” block18 comprising banks 22, sense amps 24 and I/O gating 26 similar to thosefound in other types of DRAM devices, and a control logic block innormal mode 19 which permits an external controller 20 to access thecore 18. The RDRAM core 18 is internally configured as 32 banks 22. Eachbank 22 has 32,768 144-bit storage locations.

FIG. 3 is a diagram indicating that each of the banks 22 is organized as512 rows 28 by 64 columns 30 by 144 bits 32. The 144 bits 32 in eachcolumn 30 are serially multiplexed onto the RDRAM's I/O pins as eight18-bit words 34. The most significant bits 17–9 are communicated on I/Opins DQA <8:0>, and the least significant bits 8–0 are communicated onthe I/O pins DQB <8:0>. The nine bits on each set of pins are output orinput on successive clock edges so that the bits in the eight words aretransferred on eight clock edges.

The control logic block 19 in FIG. 2 receives the CMD, SCK, SIO0, andSIO1 strobes that supply the RDRAM configuration information to thecontroller 10, and that select the operating modes of the RDRAM device10. The CFM, CFMN, CTM and CTMN pins generate the internal clocks usedto transmit read data, receive write data, and receive the row andcolumn pins used to manage the transfer of data between the banks 22 andthe sense amps 24 of the RDRAM 10.

Address information 16 is passed to the RDRAM device 10 from the CPU 11via eight RQ pins 36 as illustrated in FIG. 4. The RQ pins 36 aredivided into two groups. Three ROW pins 38 are de-multiplexed into rowpackets 40 that manage the transfer of data between the banks 22 and thesense amps 24. Five COL pins 42 are de-multiplexed into column packets44 and manage the transfer of data between the data pins and the senseamps 24 of the RDRAM 10. More detailed information on the operation ofRDRAM can be found in Reference A, Direct RDRAM Preliminary Information,Document DL0059 Version 0.9 by Rambus Inc. which is incorporated hereinby reference.

Semiconductor chips, such as an RDRAM device 10, contain circuitelements formed in the semiconductor layers which make up the integratedcircuits. FIGS. 5A and 5B illustrate a semiconductor chip with exposedbonding pads 46 made of metal, such as aluminum or the like that areformed as terminals of integrated circuits. In normal operation, thecontrol signals 14, the address signals 16, and the data 17 areexchanged with the CPU 11 through connections at these bonding pads 46.

In the manufacturing process, a large number of semiconductor chips,each having a predetermined circuit pattern, are formed on asemiconductor wafer 48 such as that shown in FIG. 6. FIG. 6 illustratesthe semiconductor wafer 48 prior to being diced into individualsemiconductor chips. Although FIG. 6 only shows a relatively smallnumber of semiconductor chips on the wafer, one skilled in the art willappreciate that many semiconductor chips can be cut from a single wafer.The semiconductor chips 10 are subjected to electrical characteristictests while they are on the wafer 48 through the use of a testingapparatus, e.g., a wafer probe 50 having a plurality of pins 52. Notethat only the head of the wafer probe 50 is shown in FIG. 6. Wafer probetesting is commonly used to quality sort individual semiconductor chipsbefore they are diced from the wafer 48. The primary goal of wafer probetesting is to identify and mark for easy discrimination defective chipsearly in the manufacturing process. Wafer testing significantly improvesmanufacturing efficiency and product quality by detecting defects at theearliest possible stages in the manufacturing and assembly process. Insome circumstances, wafer probe testing provides information to enablecertain defects to be corrected.

FIG. 7 shows a plurality of the conductive pins 52 of the wafer probe 50of FIG. 6. The pins have respective tip ends 54 positionally adjusted toalign with the bonding pads 48 of the RDRAM device 10 to be tested. Awafer probe 50 has a limited number of pins 52 (e.g., 100 pins)available to supply the test signals to the RDRAM device 10 in the wafer48. The RDRAM devices 10 could be tested in their normal mode, but thiswould require in excess of 40 pins 52 on the wafer probe 50 to test eachchip 10. Others have recognized the benefits of creating a special testmode that enables a semiconductor chip such as an RDRAM device 10 to betested with fewer pins. Therefore, one skilled in the art will recognizethat it is not required to have a pin 52 for every bonding pad 48 on thechip 10. However, prior testing methodology for RDRAM devices 10requires at least 34 pins 52 on the wafer probe 50 to test each RDRAMdevice 10. Consequently, the 100 pin wafer probe is restricted to test,at most, two semiconductor chips at one time. As a result, theproduction time and chip costs are negatively impacted by thislimitation.

As set forth above, the prior art method of wafer testing RDRAM chipsrequires 34 pins 52 to test each RDRAM device 10, of which 18 pins areaddress and data pins. Following this method, the first operation inselecting the address on the RDRAM core entails precharging the bank 22.Precharging is necessary because adjacent banks 22 share the same senseamps 24 and cannot, therefore be simultaneously activated. Precharging aparticular bank 22 deactivates the particular bank and prepares thatbank 22 and the sense amps 24 for subsequent activation. For example,when the row 28 in the particular bank 22 is activated, the two adjacentsense amps 24 are connected to or associated with that bank 22, andtherefore are not available for use by the two adjacent banks.Precharging the bank 22 also automatically causes the two adjacent banksto be precharged, thereby ensuring that adjacent banks are not activatedat the same time.

Selecting one of the 32 banks 22 to precharge requires five address bitsto specify the bank address. These address bits are provided in a firstcontrol signal. The next operation in selecting an address is activatinga row 28 in a selected bank using a second control signal. Thisoperation requires nine address bits to select one of the 512 rows 28,and five address bits to select one of the 32 banks 22, for a total of14 address bits. The next operation reads a column 30 in an open bankusing a third control signal. This operation requires five bank bits.This operation also requires six column bits to select one of the 64columns 30.

Reducing the number of address bits required to specify the addresslocation to be tested reduces the number of pin connections 52 requiredon the wafer probe 50 to test each individual RDRAM device 10. Reducingthe required number of pin connections 52 therefore allows more devices10 to be tested at the same time, thus permitting an important reductionin production time and chip costs. As chip sizes continue to decrease,there is a corresponding increase in the number of chips on eachsemiconductor wafer to be tested. Therefore, the ability to test anincreased number of devices at the same time grows in importance.

SUMMARY OF THE INVENTION

The invention comprises a method of testing computer memory devices,such as Rambus DRAM. The method requires fewer pin connections to testeach chip on a semiconductor wafer than previously known methods. Thetest is performed on a semiconductor wafer using a wafer probe. Thenumber of pins required is reduced by using a trailing edge of aprecharge clock to latch the bank address, thus eliminating the need toperform this function on a later step. In combination with such use ofthe precharge clock's trailing edge, the number of pins required isfurther reduced by dividing the chip to be tested into a plurality ofarray cores and compressing the output data so that only one data pinper array core is required. By reducing the pin count, more DRAMs can betested at the same time, thus reducing the overall test cost and timefor testing a complete wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a RDRAM device as part of acomputer system.

FIG. 2 is a functional block diagram illustrating the RDRAM chipconfiguration in the normal mode.

FIG. 3 is a conceptual drawing illustrating the RDRAM bank configured inrows, columns, words, and bits in the normal mode.

FIG. 4 is a conceptual drawing illustrating RQ pins delivering theaddress information of FIGS. 1 and 2.

FIG. 5A is a top plan view of a RDRAM chip illustrating the bondingpads.

FIG. 5B is a side elevation of the RDRAM of FIG. 5A.

FIG. 6 is a perspective view of a RDRAM semiconductor wafer comprising aplurality of chips with a wafer probe.

FIG. 7 is a top plan view of the bonding pads of a RDRAM chip alignedwith the conductive pins which are connected to a wafer probe.

FIG. 8 is a functional block diagram illustrating the RDRAM chipconfiguration in the DFT mode.

FIGS. 9A and 9B are conceptual drawings, illustrating the RDRAM bankconfigured in rows, columns, words, and bits and being further dividedso that the data from two rows can be compressed for 2× row compressionand output compressed into a single DQ for DQ compression.

FIG. 10 is a block diagram illustrating the RDRAM core divided up intofour quadrants with a single DQ output after DQ compression.

FIG. 11 is a timing diagram illustrating a typical write cycle in theDFT mode.

FIG. 12 is a timing diagram illustrating a typical read cycle in the DFTmode.

FIG. 13 is a timing diagram illustrating the compressed data output fora DQ in a window manner showing a fault detection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The RDRAM in accordance with the invention has two modes of operation:(1) a high speed packet mode for normal operation; and (2) a low speedasynchronous mode for testing, which bypasses the packetizing hardware,often called “design for test” circuits or DFT. This second mode, shownas a block diagram in FIG. 8 is realized by including DFT mode controllogic 58 and data compression logic 59 in the RDRAM device 10 tofacilitate testing. In one embodiment of the invention, in the DFT testmode, the RDRAM behaves similar to an asynchronous DRAM, although datais still input/output in bursts of eight.

As shown in FIG. 8, the RDRAM comprises three major blocks: a “core”block 18, the control logic block in DFT mode 58 and the DataCompression/Expansion Logic box 59. As shown in FIGS. 9A and 9B, thecore 18 is internally configured as 32 banks 22 organized as 512 rows 28by 64 columns 30 by 144-bit storage locations. The 144 bits aremultiplexed as eight 18-bit words. The core is further divided fortesting purposes as will be discussed below.

The DFT control logic 58 receives a number of signals from the waferprobe 50, including, TestBSENSE, TestPRECH, TestWRITE, TestCOLLAT,TestCLK_(—)R/W, SIO0, SIO1, CMD, SCK and Burn PRECH_(—)EN. The DataCompression/Expansion Logic 59 compresses data so that only four datapins are required, as will be discussed below.

The pins required for the DFT mode of operation are a subset of the pinsused in the normal mode of operation. Many of the functions of thenormal mode pins are redefined (as discussed below) for the DFT mode.The mapping of the normal mode pins to the DFT mode functions isillustrated below in Table 1.

TABLE 1 DFT Pin Mapping Pin DFT Function SCK SCK CMD CMD SIO<1:0>SIO<1:0> CFM/CTM TestClkR/W RQ<0> TestBSENSE RQ<1> TestPRECH RQ<2>TestWrite RQ<3> TestCOLLAT DQB<2:0> ADR<2:0> DQA<3:0> ADR<6:3> DQB<3>ADR<7> DQB<6> ADR<8> DQB<8> Burn PRECH_(—)EN DQA<5:4> DQ<1:0> DQB<5:4>DQ<3.2> CFMN/CTMN VCC/2 VCMOS VCMOS

To test a specific location in the core block 18 of the RDRAM device 10,the location must be referenced by its bank address, row address, andcolumn address. In the normal configuration of a 144 Mbit RDRAM deviceas illustrated in FIG. 3, selecting the bank address of one of the 32banks requires five address bits, selecting a row address of one of the512 rows in a bank requires nine address bits, and selecting a columnaddress of one of the 64 columns in a bank requires six address bits. Inaccordance with the present invention, the 144 Mbit RDRAM device iswafer tested using DQ compression and 2× row compression.

In a further embodiment, a 288 Mbit RDRAM device can be tested accordingto the invention as well. In the normal configuration of a 288 MbitRDRAM device, the RDRAM core block 18 is internally configured as 32banks 22. Each bank 22 is organized as 512 rows 28 by 128 columns 30 by144 bits 32. Selecting the bank address of one of the 32 banks requiresfive address bits, selecting a row address of one of the 512 rows in abank requires nine address bits, and selecting a column address of oneof the 128 columns in a bank requires seven address bits. In accordancewith the present invention, the 288 Mbit RDRAM device can be wafertested using either DQ compression or DQ compression and 2× rowcompression.

In DQ compression, the RDRAM device 10 is divided into four quadrants,60A, 60B, 60C, and 60D, as illustrated in FIG. 10, with each quadrantcorresponding to a respective 36 megabit array core 61A, 61B, 61C, and61D. Each array core 61A, 61B, 61C, and 61D is an independent repairregion. The lower two quadrants, 60A and 60B, comprise banks 0–15. Theupper two quadrants, 60C and 60D, comprise banks 16–31. This division isbased on physical design parameters of the RDRAM device 10. The lowerleft quadrant 60A comprises bits 9–17 of banks 0–15. The lower rightquadrant 60B comprises bits 0–8 of banks 0–15. The upper left quadrant60C comprises bits 9–17 of banks 16–31. The upper right quadrant 60Dcomprises bits 0–8 of banks 16–31. As discussed below, for testing, onlya single bit of data is transferred into and out of each quadrant 60A,60B, 60C, and 60D. In particular, as will be discussed below, a data bitDQ0 is used to test the upper left quadrant 60C. A data bit DQ1 is usedto test the upper right quadrant 60D. A data bit DQ2 is used to test thelower left quadrant 60A. A data bit DQ3 is used to test the lower rightquadrant 60B. Therefore, only four data bits are required to test theentire memory. Note further that the upper banks (16–31) and the lowerbanks (0–15) have separate data connections in the DFT mode. Thus, themost significant bank bit that distinguishes the upper and lower sets ofbanks is not required, and the number of bank bits is reduced from fivebits to four bits.

In one embodiment of the invention using DQ compression and 2× rowcompression, the 2× row compression further reduces the number of bankaddress bits required. In particular, the data from corresponding rowsin two alternating banks (e.g., bank n with bank n+2 and bank n+16 withbank n+18) are combined as shown in FIGS. 9A and 9B so that the data aretransferred to and from both rows using a common DQ bit. This reducesthe number of selectable banks in each quadrant from sixteen to eight.Thus, only three bank bits are required to select one of the eight banksin each quadrant.

The data from the two rows of the alternating banks are transferred(either written to the memory or read from the memory) one byte at atime, as in the normal mode. However, because only one data pin isavailable for each quadrant 60A, 60B, 60C, and 60D, the nine bits ofdata from each of the two rows (18 bits of data in all) in each quadrantare combined into a respective single bit (i.e., DQ0, DQ1, DQ2, or DQ3).Thus, for each quadrant the data from a column in the two rows areoutput as a sequence of eight single data bits.

The compression of the data bits is performed by the datacompression/expansion logic 59. Each quadrant 60A, 60B, 60C, and 60D canhave an associated data compression/expansion logic 59A, 59B, 59C, and59D as illustrated in FIGS. 9A and 9B. Data are written to the memory byapplying a data bit to each of the compressed data pins (i.e., to DQ0,DQ1, DQ2, DQ3). On each clock edge the data compression/expansion logic59 fans out the single data bit to the eighteen data locations addressedby the bank, row and column bits. Thus, the same data are written intoall eighteen locations. Thereafter, when the memory locations are readto test the integrity of the memory, the data from the eighteenlocations read during each clock edge are compared to determine if anylocation has a different data output. If the data are the same, theoutput on the DQ line has a first constant state (e.g., a logic one or alogic zero in accordance with the data written during the writeoperation) to indicate pass. If any bit in any of the eighteen locationsis different, the data output on the DQ line is forced to have atransition to indicate a failure.

In one embodiment for testing a 288 Mbit RDRAM device, the result of theDQ compression and the 2× row compression is that the array cores 61A,61B, 61C and 61D are configured as 8 banks by 512 rows by 128 columns byeight four-bit bytes. Therefore, only three bank select bits, nine rowaddress bits, and seven column address bits are required to identify aparticular location in the array core. This results in the ability totest each RDRAM device 10 using only nine pins on the wafer probe 50 fordefining a specific address location. When the row is activated, ninerow address bits identify one of the 512 rows. When a column in an openbank is read, the seven column bits identify the column in the bank tobe written to or read from.

FIG. 11 is a timing diagram that illustrates a typical write cycle thatis used to select the bank for row access and the bank for columnaccess, row address, column address, and strobe in the data. FIG. 12 isa timing diagram that similarly illustrates a typical read cycle. InFIGS. 11 and 12, address pins 64, 68, and 70 refer to subdivisions ofthe nine address pins used to identify a particular location in thearray core. Address pins 64 represent Addr<8:6> (three address pins 8,7, and 6). Address pins 68 represent Addr<5:1> (five address pins 5, 4,3, 2, and 1). Address pins 70 represent Addr<0> (one address pin 0).

In the write and read cycles depicted in FIGS. 11 and 12, respectively,a precharge clock, TestPRECH 62, is used to select the bank address. Theleading edge of TestPRECH 62 is used to precharge the bank designated bythe bank address present on the address pins 64. Precharging the bankprepares the bank and the sense amps for activation. Since adjacentinner banks share the same sense amps, adjacent banks cannot beactivated at the same time. Precharging any bank automatically causesadjacent banks to be precharged also, thereby ensuring that adjacentbanks are not open at the same time. This happens in all modes ofoperation, not just the DFT mode.

On the falling edge of TestPRECH 62, the bank corresponding to the bankaddress on the address pins 64 is latched. This latched bank addressrepresents the bank that will be activated the next time TestBSENSE ispresented. Multiple banks can be active at any one time. That is, bankspreviously activated and not subsequently deactivated by prechargingremain active in addition to the newly activated bank. Precharging banksand latching banks are accomplished using different edges of the sameTestPRECH signal 62. Thus, the present invention eliminates the need toprovide separate control signals for the precharge function and thelatching function.

Next, a row address is selected using address pins and a row senseclock, TestBSENSE 66. TestBSENSE 66 causes the selected row of thelatched (i.e., active) bank to be sensed. The row address to be sensedis the address present on the address pins 64, 68 and 70 at the fallingedge of TestBSENSE 66. Because there are 512 rows, nine address pins arerequired to select the row to be tested. Because the bank was latchedusing the other edge of the TestPRECH 62, it is not required to select abank in this operation. Thus, unlike other known methods, the bankselect bits do not have to be applied at this time and only the nineaddress bits need to be applied.

Data are then either read from or written to the column in accordancewith the address present on the address pins at the rising edge of acolumn latch clock, TestCOLLAT 72. The row address of the bank to beopened is presented on the falling edge of TestBSENSE 66. The address ofthe column to be accessed is presented on the rising edge of TestCOLLAT72. In one embodiment of the invention, if a new bank is to be opened,then the address of that bank must be the same as the bank of the columnto be accessed. As a result, nine address bits are sufficient to providethe necessary address bits to identify any location in the array core.

In a further embodiment, the bank must be one of the banks that wasactive when TestBSENSE 66 was applied. A TestWrite clock 74 determineswhether the operation performed at TestCOLLAT 72 time is a read or awrite function. If TestWrite=1 at the rising edge of TestCOLLAT 72, thenthe data present in a write buffer are written to the RDRAM core. IfTestWrite=0 at the rising edge of TestCOLLAT 72, then the data are readfrom the RDRAM core to a read buffer.

FIGS. 11 and 12 show a TestClkR/W clock 76 strobing data into the writebuffer or out of the read buffer depending on the state of TestWrite 74.If TestWrite=1, then data are input into the write buffer from thetester on sequential edges of TestClkR/W 76, beginning with the firstfalling edge. Eight clock edges transfer data. It takes a total of sixTestClkR/W 76 cycles to completely load the write buffer. Additionalclock cycles will initiate another load sequence. A load sequence is notterminated until the exact number of clock cycles are provided. IfTestWrite=0, then data are read from the read buffer to the external buson each edge of TestClkR/W 76, beginning with the second falling edge.Eight clock edges transfer the data. It takes a total of six TestClkR/W76 cycles to completely empty the read buffer. The chip under testremains in the output mode until all data are read out of the readbuffer. Any additional clock cycles initiates a new read sequence. Notethat any transition on TestClkR/W 76 initiates a read or write sequencedepending on the state of TestWrite 74.

FIG. 13 is a timing diagram that illustrates the compressed data beingoutput in a window manner when reading the compressed DQs. If theexpected data is a “0”, then the DQ will be low during the entirewindow. A failure is indicated if the wrong data is present, or if adata transition is detected during the window. If the expected data is“1”, then the DQ should remain high throughout the window.

If a fault is indicated, it is not necessary to determine which bitfailed, it is sufficient to localize the fault to a row. The tester hasthe capability to reconfigure the chip so that a spare row is used toreplace the row with the fault. The technology for such reconfigurationis well known in the field.

Note that by reducing the required address bits to three and by usingboth edges of the TestPRECH control signal, the maximum number ofaddress bits required is nine, which with the addition of the four databits, totals thirteen. This is significantly fewer than the eighteendata and address bits used in other known test methods.

Although specific implementations and operation of the invention havebeen described above with reference to specific embodiments, theinvention may be embodied in other forms without departing from thespirit or central characteristics of the invention. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning of equivalency of the claims are to beembraced within their scope.

1. A method of testing a computer memory device, the method comprising:outputting to a memory device a control signal having a precharge signaldefined by a first portion of the control signal and a latch signaldefined by a second portion of the control signal; outputting to thememory device a first bank address signal defining a first bank oflocations, within the memory device, to be precharged; outputting to thememory device a second bank address signal defining a second bank oflocations, within the memory device, to be latched; outputting to thememory device a row address signal and a column address signal, the rowaddress signal and the column address signal defining a test locationwithin the latched bank of locations; receiving data stored at the testlocation; and comparing the received data with test data in order totest the integrity of the memory device.
 2. The method of claim 1,wherein the act of outputting the control signal is performed through aprobe.
 3. The method of claim 2, wherein the act of outputting thecontrol signal is performed through a single pin of the probe.
 4. Themethod of claim 1, wherein the memory device comprises a Rambus dynamicrandom access memory (RDRAM).
 5. The method of claim 1, wherein the testdata comprises data that was previously stored in the test location. 6.The method of claim 1, wherein the first portion of the control signalis a leading edge of the control signal.
 7. The method of claim 6,wherein the second portion of the control signal is a trailing edge ofthe control signal.
 8. A method of testing a plurality of computermemory devices, the method comprising: outputting to each of a pluralityof memory devices a control signal having a precharge signal defined bya first portion of the control signal and a latch signal defined by asecond portion of the control signal; outputting to each of theplurality of the memory devices a row address signal and a columnaddress signal, the row address signal and the column address signaldefining a test location within each of the plurality of memory devices;receiving data stored at each test location within each of the pluralityof memory devices; and comparing the received data with test data inorder to test the integrity of the plurality of memory devices.
 9. Themethod of claim 8, wherein the act of outputting the control signal isperformed through a probe.
 10. The method of claim 8, wherein theplurality of memory devices comprises at least three memory devices. 11.The method of claim 8, wherein the plurality of memory devices comprisesRambus dynamic random access memory (RDRAM).
 12. The method of claim 8,wherein the first portion of the control signal is a leading edge of thecontrol signal.
 13. The method of claim 12, wherein the second portionof the control signal is a trailing edge of the control signal.
 14. Anapparatus for testing a computer memory device, the apparatuscomprising: means for outputting to a memory device being tested acontrol signal having a precharge signal defined by a first portion ofthe control signal and a latch signal defined by a second portion of thecontrol signal, and wherein said means for outputting is furtherconfigured to output to the memory device address bits defining at leastone location within the memory device; means for reading data from thememory device, wherein the data is stored at the at least one locationdefined by the address bits; and means for comparing the data read fromthe memory device with test data in order to test the integrity of thememory device.
 15. The apparatus of claim 14, wherein the memory devicecomprises a Rambus dynamic random access memory (RDRAM).
 16. Theapparatus of claim 14, wherein the means for outputting comprises awafer probe.
 17. The apparatus of claim 14, wherein the first portion ofthe control signal is a leading edge of the control signal.
 18. Theapparatus of claim 14, wherein the second portion of the control signalis a trailing edge of the control signal.